Consider a tennis player who hits a serve at 140 mi/h (63 m/s). Estimate the average force exerted by the racket on the ball (m = 57 g).

You will need to estimate the collision time, that is, the time two objects are in contact during a collision. For comparison, the collision time for a baseball–bat collision is approximately 0.001 s, while the time for a tennis racket–ball collision is about 0.01 s. In general, hard things produce short contact times and soft things lead to long contact times.